Different optical films such as polarizing films and phase difference films used for liquid crystal displays are required to have no unevenness in thickness. In particular, monitors and television sets have become large and had higher definition, and which are requiring better quality.
In a manufacturing device of optical films based on the melt-casting film forming method, molten film-constituting-material containing a thermoplastic resin is discharged in a film shape from a flow casting die, and the film-shaped molten article is cooled and solidified by being sandwiched between a pair of rotation rolls. However, there is an issue that the flow casting die is heated to a high temperature, thereby making a large temperature difference between the flow casting die and the rotation rolls, then generating a ascending airflow between the flow casting die and the pair of rotation rolls, and airflows blow in toward the flow casting die from both sides in the width direction. The airflows flowing in hit the surface of the film-shaped molten article to generate a temperature distribution on the surface, thereby causing unevenness in thickness.
In such melt-casting film forming method, as a method for improving the unevenness in thickness there is proposed a technique in which a shielding plate is provided at each end between the width-direction end of the rotation roll and the width-direction end of the film-shaped molten article, perpendicularly to the surface of the molten article (Patent Document 1). In this technique, the shielding plates prevent the airflows from hitting the width-direction ends of the film-shaped molten article. However, gaps between the shielding plates and the rotation roll are not avoidable, and it is impossible to perfectly prevent the airflows from flowing in; therefore, the unevenness in thickness of optical films cannot be sufficiently avoided.